Catalyst and a Process for the Production of Ethylenically Unsaturated                        Carboxylic Acids or Esters

ABSTRACT

A catalyst has a modified silica support and comprises a modifier metal, zirconium and/or hafnium, and a catalytic metal on the modified support. The catalyst has at least a proportion, typically, at least 25%, of modifier metal present in moieties having a total of up to 2 modifier metal atoms. The moieties may be derived from a monomeric and/or dimeric cation source.A method of production:provides a silica support with isolated silanol groups with optional treatment to provide isolated silanol groups (—SiOH) at a level of &lt;2.5 groups per nm2;contacting the optionally treated silica support with a monomeric zirconium or hafnium modifier metal compound to effect adsorption onto the support; andoptionally calcining the modified support for a time and temperature sufficient to convert the monomeric zirconium or hafnium compound adsorbed on the surface to an oxide or hydroxide of zirconium or hafnium in preparation for catalyst impregnation.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation application and claims benefit of andpriority to U.S. patent application Ser. No. 16/646,763 filed on Mar.12, 2020.

The present invention relates to a modified silica catalyst support, acatalyst incorporating the modified silica support and a process for theproduction of ethylenically unsaturated carboxylic acids or esters,particularly α, β unsaturated carboxylic acids or esters, moreparticularly acrylic acids or esters such as (alk)acrylic acids or alkyl(alk)acrylates particularly (meth)acrylic acids or alkyl (meth)acrylatessuch as methacrylic acid (MA) and methyl methacrylate (MMA) by thecondensation of carboxylic acid or esters with formaldehyde or a sourcethereof such as dimethoxymethane in the presence of such catalysts, inparticular, by the condensation of propionic acid or alkyl estersthereof such as methyl propionate with formaldehyde or a source thereofin the presence of such modified silica supported catalytic metalcatalysts. The invention is therefore particularly relevant to theproduction of methacrylic acid (MAA) and methyl methacrylate (MMA).

As mentioned above, such unsaturated acids or esters may be made by thereaction of a carboxylic acid or ester and suitable carboxylic acids oresters are alkanoic acids (or esters) of the formula R³—CH₂—COOR⁴, whereR³ and R⁴ are each, independently, a suitable substituent known in theart of acrylic compounds such as hydrogen or an alkyl group, especiallya lower alkyl group containing, for example, 1-4 carbon atoms. Thus, forinstance, methacrylic acid or alkyl esters thereof, especially methylmethacrylate, may be made by the catalytic reaction of propionic acid,or the corresponding alkyl ester, e.g. methyl propionate, withformaldehyde as a methylene source in accordance with the reactionsequence 1.

An example of reaction sequence 1 is reaction sequence 2

The above reaction sequences are typically effected at an elevatedtemperature, usually in the range 250-400° C., using and acid/basecatalyst. Where the desired product is an ester, the reaction istypically effected in the presence of the relevant alcohol in order tominimise the formation of the corresponding acid through hydrolysis ofthe ester. Also for convenience it is often desirable to introduce theformaldehyde in the form of a complex of formaldehyde with methanol.Hence, for the production of methyl methacrylate, the reaction mixturefed to the catalyst will generally consist of methyl propionate,methanol, formaldehyde and water.

A known production method for MMA is the catalytic conversion of methylpropionate (MEP) to MMA using formaldehyde. A known catalyst for this isa caesium catalyst incorporating a support, for instance, silica.

WO1999/52628 discloses a catalyst for use in the production of α, βunsaturated carboxylic acids or esters by the condensation of propionicacid or the corresponding alkyl ester wherein the catalyst comprisesalkali metal doped silica impregnated with at least one modifier elementwherein the modifier element is selected from a group consisting ofboron, aluminium, magnesium, zirconium and hafnium, preferably zirconiumand/or aluminium and/or boron and the alkali metal is selected frompotassium, rubidium or caesium, preferably caesium.

WO2003/026795 discloses a catalyst for use in aldol condensationsincluding the production of α, β unsaturated carboxylic acids by thecondensation of propionic acid or propionic ester, olefinpolymerisation, dehydration, hydroxylation and isomerisation wherein thecatalyst comprises a silica-metal hydrogel impregnated with a catalyticmetal wherein the metal of the hydrogel is selected from a groupconsisting of zirconium, titanium, aluminium and iron, preferablyzirconium, and the catalytic metal is selected from a group consistingof alkali metals and alkaline earth metals, preferably caesium.

The present inventors have now discovered that catalysts comprisingcertain metal modified silica supports, and containing a catalyticmetal, provide a high level of selectivity in the condensation ofmethylene sources such as formaldehyde with a carboxylic acid or alkylester such as methyl propionate when at least a proportion of themodifier metal is incorporated or present in the support in the form ofmetal species having a total of up to two zirconium and/or hafniumatoms.

It is known from Yung-Jin Hu et al, J. Am. Chem. Soc. Volume 135, 2013,p 14240, that zirconium is capable of forming large clusters insolution. Zr-18 clusters are typical.

However, the current inventors have surprisingly found that when themodified silica support comprises zirconium and/or hafnium oxidemoieties derived from a monomeric and/or dimeric modifier metal cationsource such as a compound thereof at the commencement of themodification, rather than such larger clusters, there has been found tobe an improvement in catalytic metal binding to the modified support andthereafter higher selectivity for the production of unsaturatedcarboxylic acid or esters by condensation of the corresponding acid orester with a methylene source such as formaldehyde. Furthermore, theinventors have found that the modified silica supports providing thesehigh selectivities contain monomeric or dimeric modifier metal atomsafter deposition/adsorption onto the surface of the silica.

Still further, the present inventors have found that when such modifiedsilica supports are used, the rate of catalyst surface sintering hasbeen found to be retarded and loss of surface area upon which thecatalytic reaction takes place during the condensation reaction isreduced.

Therefore, catalysts comprising such modified silica supports andcontaining a catalytic metal are remarkably effective catalysts for theproduction of α, β ethylenically unsaturated carboxylic acids or estersby condensation of the corresponding acid or ester with a methylenesource such as formaldehyde providing several advantages such as highlevels of selectivity and/or reduced sintering of the catalyst surface.

Therefore, according to a first aspect of the present invention, thereis provided a catalyst comprising

a modified silica support,the modified silica support comprising a modifier metal;and a catalytic metal on the modified silica support,wherein the modifier metal is selected from one or more of zirconiumand/or hafnium,characterised in that at least a proportion, typically, at least 25%, ofthe said modifier metal is present in the form of modifier metalmoietieshaving a total of up to 2 modifier metal atoms.

According to a further aspect of the present invention, there isprovided a catalyst comprising

a modified silica support,the modified silica support comprising a modifier metal;and a catalytic metal on the modified silica support,wherein the modifier metal is selected from one or more of zirconiumand/or hafnium,characterised in that at least a proportion, typically, at least 25%, ofthe said modifier metal is present in the form of modifier metalmoieties derived from a monomeric and/or dimeric modifier metal cationsource.

The monomeric and/or dimeric modifier metal contacts the silica supportas a monomeric and/or dimeric zirconium or hafnium modifier metal cationsource such as a compound thereof in solution to effect adsorption ofthe said modifier metal onto the support to thereby form the modifiermetal moieties. A suitable source may be a complex of the modifiermetal, more typically, a ligand complex in solution.

According to a second aspect of the present invention, there is provideda modified silica support for a catalyst comprising

a silica support anda modifier metalwherein the modifier metal is selected from one or more of zirconiumand/or hafnium,characterised in that at least a proportion, typically, at least 25%, ofthe said modifier metal is present in the form of modifier metalmoietieshaving a total of up to 2 modifier metal atoms.

According to a third aspect of the present invention, there is provideda modified silica support for a catalyst comprising

a silica support anda modifier metalwherein the modifier metal is selected from one or more of zirconiumand/or hafniumcharacterised in that at least a proportion, typically, at least 25%, ofthe said modifier metal is present in the form of modifier metalmoieties derived from a monomeric and/or dimeric modifier metal cationsource at the commencement of the modification.

The modified silica support herein is modified by the modifier metal.Typically, the modifier metal is an adsorbate adsorbed on the silicasupport surface. The adsorbate may be chemisorbed or physisorbed ontothe silica support surface, typically, it is chemisorbed thereon. Themodifier metal moieties are generally modifier metal oxide moieties.

The silica support is generally in the form of a silica gel, moretypically, a xerogel or a hydrogel

Typically, the modifier metal is adsorbed on the silica gel supportsurface. Therefore, typically, said modifier metal is present on themodified silica gel support surface in the form of metal oxide moieties.

Alternatively, the modifier metal may be present in the support in theform of a co-gel. In such a case the modified silica support is asilica-metal oxide gel, typically, comprising zirconium and/or hafniumoxide moieties.

Typically, the modifier metal is present in the modified silica supportin an effective amount to reduce sintering and improve selectivity ofthe catalyst. Typically, at least 30%, such as at least 35%, morepreferably at least 40%, such as at least 45%, most suitably at least50%, such as at least 55%, for example at least 60% or 65%, and mostpreferably at least 70% such as at least 75% or 80%, more typically, atleast 85%, most typically, at least 90%, especially, at least 95% of themodifier metal in the modified silica support is in moieties having atotal of 1 and/or 2 metal atoms, especially, in moieties having a totalof 1 metal atom or is derived from a monomeric and/or dimeric metalcompound at the commencement of the modified silica formation at suchlevels.

For the avoidance of doubt, modifier metal moieties having a total of 1metal atom are considered monomeric and having a total of 2 metal atomsare dimeric. In particularly preferred embodiments, such as at least35%, more preferably at least 40%, such as at least 45%, most suitablyat least 50%, such as at least 55%, for example at least 60% or 65%, andmost preferably at least 70% such as at least 75% or 80%, moretypically, at least 85%, most typically, at least 90%, especially, atleast 95% of the modifier metal is present in monomeric metal moieties,or, in any case, is typically derived from zirconium and/or hafniumcompounds at the commencement of the modification having such levels ofmodifier metal as monomeric compounds. Generally, the modifier metalmoieties on the silica are modifier metal oxide moieties.

Clusters of zirconium and/or hafnium larger than 2 metal atoms dispersedthroughout the support such as a hydrogel support, have surprisinglybeen found to decrease reaction selectivity for the production of α, βethylenically unsaturated carboxylic acids or esters by condensation ofthe corresponding acid or ester with a methylene source such asformaldehyde. Such large clusters have also surprisingly been found toincrease sintering of the modified silica particles relative to clustersof modifier metal with 2 or 1 metal atom(s) thereby reducing the surfacearea which lowers strength and reduces the life of the catalyst beforeactivity becomes unacceptably low. In addition, selectivity is oftenlower, depending on the nature of the cluster of the modifier metal.

Typically, the modifier metal is dispersed throughout the support in asubstantially homogeneous manner.

Typically, the modified silica support is a xerogel. The gel may also bea hydrogel or an aerogel.

The gel may also be a silica-zirconia and or silica-hafnia co-gel. Thesilica gel may be formed by any of the various techniques known to thoseskilled in the art of gel formation such as mentioned herein. Typically,the modified silica gels are produced by a suitable adsorption reaction.Adsorption of the relevant metal compounds such as zirconium and/orhafnium compounds to a silica gel such as a silica xerogel to formmodified silica gel having the relevant modifier metal moieties is asuitable technique.

Methods for preparing silica gels are well known in the art and somesuch methods are described in The Chemistry of Silica: Solubility,Polymerisation, Colloid and Surface Properties and Biochemistry ofSilica, by Ralph K. Iler, 1979, John Wiley and Sons Inc., ISBN0-471-02404-X and references therein.

Methods for preparing silica-zirconia co-gels are known in the art andsome such methods are described in U.S. Pat. No. 5,069,816, by Bosman etal in J Catalysis Vol. 148 (1994) page 660 and by Monros et al. in JMaterials Science Vol. 28, (1993), page 5832.

In preferred embodiments, the modified silica support is not formed byco-gelation i.e. not a silica-zirconia, silica-hafnia orsilica-zirconia/hafnia formed by co-gelation such as by mixing of sodiumsilicate solution with modifier metal complexes in sulphuric acidsolution. In such embodiments, the zirconium and/or hafnium is typicallyincorporated as an adsorbate on the silica support surface.

Preferably, the modified silica supported catalyst and modified silicasupport according to any aspect of the present invention may besubstantially free, may be essentially free or may be completely free offluoride. Fluoride may be present in trace amounts because ofunavoidable contamination from the environment. By “substantially free”we mean to refer to catalysts and supports containing less than 1000parts per million (ppm) of fluoride. By “essentially free” we mean torefer to catalysts and supports containing less than about 100 ppm offluoride and by “completely free” we mean to refer to catalystscontaining less than 200 parts per billion (ppb) of fluoride.

Advantageously, when at least a proportion of the modifier metalincorporated into the modified silica of the above aspects of thepresent invention is derived from a monomeric and/or dimeric modifiermetal cation source at the commencement of the modified silicaformation, there has been found to be improved reaction selectivityand/or reduced rate of sintering of the catalyst surface during theproduction of α, β ethylenically unsaturated carboxylic acids or esters.

Metal and metal oxide moieties in the modified silica support accordingto the present invention relate to zirconium and/or hafnium and zirconiaand/or hafnia, not to silica.

Preferably, the level of modifier metal present in the modified silicaor catalyst may be up to 7.6×10⁻² mol/mol of silica, more preferably upto 5.9×10⁻² mol/mol of silica, most preferably up to 3.5×10⁻² mol/mol ofsilica. Typically, the level of such metal is between 0.067×10⁻² and7.3×10⁻² mol/mol of silica, more preferably, between 0.13×10⁻² and5.7×10⁻² mol/mol of silica and most preferably between 0.2×10⁻² and3.5×10⁻² mol/mol of silica. Typically, the level of modifier metalpresent is at least 0.1×10⁻² mol/mol of silica, more preferably, atleast 0.15×10⁻² mol/mol of silica and most preferably at least 0.25×10⁻²mol/mol of silica.

Preferably, when zirconium is the modifier metal, the level of zirconiummetal may be up to 10% w/w of the modified silica support, morepreferably up to 8% w/w, most preferably up to 5.5% w/w. Typically, thelevel of zirconium metal is between 0.1-10% w/w of the modified silicasupport, more preferably between 0.2-8% w/w and most preferably between0.3-5% w/w. Typically, the level of zirconium metal is at least 0.5% w/wof the modified silica support, such as 0.8% w/w, more typically, atleast 1.0% w/w, most typically, at least 1.5% w/w.

Preferably, the level of hafnium metal may be up to 20% w/w of themodified silica support, more preferably up to 16% w/w, most preferablyup to 10% w/w. Typically, the level of hafnium metal is between 0.2-20%w/w of the modified silica support, more preferably between 0.4-16% w/wand most preferably between 0.6-10% w/w. Typically, the level of hafniummetal is at least 1.0% w/w of the modified silica support, moretypically, 2.0% w/w, most typically, at least 3.0% w/w.

The silica component of the silica-zirconium oxide support may typicallyform 86.5-99.9 wt % of the modified support, more typically 89.2-99.7 wt%, most typically 93.2-99.6 wt % thereof.

The silica component of the silica-hafnium oxide support typically forms76.4-99.8 wt % of the modified support, more typically 81.1-99.5 wt %,most typically 88.2-99.3 wt % thereof.

By the term “up to 2 metal atoms” or the like as used herein, is meant 1and/or 2 metal atoms. Preferably, the modified silica support andcatalyst according to any aspects of the present invention comprisemetal moieties, typically, metal oxide moieties having up to 2 metalatoms and most preferably, 1 metal atom. Accordingly, it will beappreciated that such moieties are monomeric, or dimeric metal moieties.

Preferably, the catalytic metal may be one or more alkali metals. Thecatalytic metal is a metal other than zirconium or hafnium. Suitablealkali metals may be selected from potassium, rubidium and caesium,suitably rubidium and caesium. Caesium is the most preferred catalyticmetal.

Suitably the catalytic metals such as caesium may be present in thecatalyst at a level of at least 1 mol/100 (silicon+metal (zirconiumand/or hafnium)) mol more preferably, at least 1.5 mol/100(silicon+metal) mol, most preferably, at least 2 mol/100 (silicon+metal)mol. The level of catalytic metal may be up to 10 mol/100(silicon+metal) mol in the catalyst, more preferably, up to 7.5 mol/100(silicon+metal) mol, most preferably, up to 5 mol/100 (silicon+metal)mol in the catalyst.

Preferably, the level of catalytic metal in the catalyst is in the rangefrom 1-10 mol/100 (silicon+metal) mol, more preferably, 2-8 mol/100(silicon+metal) mol, most preferably, 2.5-6 mol/100 (silicon+metal) molin the catalyst.

Unless indicated to the contrary, amounts of alkali metal or alkalimetal in the catalyst relate to the alkali metal ion and not the salt.

Alternatively, the catalyst may have a wt % of catalytic metal in therange 1 to 22 wt % in the catalyst, more preferably 4 to 18 wt %, mostpreferably, 5-13 wt %. These amounts would apply to all alkali metals,but especially caesium.

The catalyst may comprise any suitable weight ratio of catalytic alkalimetal:zirconium and/or hafnium metal. However, typically, the weightratios for caesium:zirconium are in the range from 2:1 to 10:1, morepreferably from 2.5:1 to 9:1, most preferably from 3:1 to 8:1 in thecatalyst, for caesium:hafnium are in the range from 1:1 to 5:1, morepreferably from 1.25:1 to 4.5:1, most preferably from 1.5:1 to 4:1 inthe catalyst, for rubidium:zirconium are in the range from 1.2:1 to 8:1,more preferably from 1.5:1 to 6:1, most preferably from 2:1 to 5:1 inthe catalyst, for rubidium:hafnium are in the range from 0.6:1 to 4:1,more preferably from 0.75:1 to 3:1, most preferably from 1:1 to 2.5:1 inthe catalyst. Accordingly, the catalytic metal:modifier metal mole ratioin the catalyst is typically at least 1.4 or 1.5:1, preferably, it is inthe range 1.4 to 2.7:1 such as 1.5 to 2.1:1, especially, 1.5 to 2.0to:1, typically in this regard the modifier metal is zirconium and thecatalytic metal is caesium. Generally, herein, the catalytic metal is inexcess of that which would be required to neutralise the modifier metal.

Preferably, the catalytic metal is present in the range 0.5-7.0 mol/molmodifier metal, more preferably 1.0-6.0 mol/mol, most preferably 1.5-5.0mol/mol modifier metal.

Suitably, the catalytic metal may be incorporated into the modifiedsilica support by any method known in the art such as impregnation,co-gelation or vapour deposition with the catalytic metal.

By the term “impregnated” as used herein is included the addition of thecatalytic metal dissolved in a solvent, to make a solution, which isadded to the xerogel or aerogel, such that the solution is taken up intothe voidages within the said xerogel or aerogel.

Typically, the catalyst of the invention may be in any suitable form.Typical embodiments are in the form of discrete particles. Typically, inuse, the catalyst is in the form of a fixed bed of catalyst.Alternatively, the catalyst may be in the form of a fluidised bed ofcatalyst. A further alternative is a monolith reactor.

Where the catalysts are used in the form of a fixed bed, it is desirablethat the supported catalyst is formed into granules, aggregates orshaped units, e.g. spheres, cylinders, rings, saddles, stars, poly-lobesprepared by pelleting, or extrusion, typically having maximum andminimum dimensions in the range 1 to 10 mm, more preferably, with a meandimension of greater than 2 mm such as greater than 2.5 or 3 mm. Thecatalysts are also effective in other forms, e.g. powders or small beadsof the same dimensions as indicated. Where the catalysts are used in theform of a fluidised bed it is desirable that the catalyst particles havea maximum and minimum dimension in the range of 10-500 μm, preferably20-200 μm, most preferably 20-100 μm.

Levels of catalytic metal in the catalyst whether atoms/100 atoms(silicon+zirconium and/or hafnium) or wt % may be determined byappropriate sampling and taking an average of such samples. Typically,5-10 samples of a particular catalyst batch would be taken and alkalimetal levels determined and averaged, for example by XRF, atomicabsorption spectroscopy, neutron activation analysis, ion coupled plasmamass spectrometry (ICPMS) analysis or ion coupled plasma atomic emissionspectroscope (ICPAES).

Levels of the metal oxide of particular types in the catalyst/supportare determined by XRF, atomic absorption spectroscopy, neutronactivation analysis or ion coupled plasma mass spectrometry (ICPMS)analysis.

The typical average surface area of the modified silica supportedcatalyst according to any aspect of the invention is in the range 20-600m²/g, more preferably 30-450 m²/g and most preferably 35-350 m²/g asmeasured by the B.E.T. multipoint method using a Micromeritics Tristar3000 Surface Area and porosity analyzer. The reference material used forchecking the instrument performance may be a carbon black powdersupplied by Micromeritics with a surface area of 30.6 m²/g (+/−0.75m²/g), part number 004-16833-00.)

If the catalyst material is porous, it is typically a combination ofmesoporous and macroporous with an average pore size of between 2 and1000 nm, more preferably between 3 and 500 nm, most preferably between 5and 250 nm. Macropore size (above 50 nm) can be determined by mercuryintrusion porosimetry using NIST standards whilst theBarrett-Joyner-Halenda (BJH) analysis method using liquid nitrogen at77K is used to determine the pore size of mesopores (2-50 nm). Theaverage pore size is the pore volume weighted average of the pore volumevs. pore size distribution.

The average pore volume of the catalyst particles may be less than 0.1cm³/g but is generally in the range 0.1-5 cm³/g as measured by uptake ofa fluid such as water. However, microporous catalysts with very lowporosity are not the most preferred because they may inhibit movement ofreagents through the catalyst and a more preferred average pore volumeis between 0.2-2.0 cm³/g. The pore volume can alternatively be measuredby a combination of nitrogen adsorption at 77K and mercury porosimetry.The Micromeritics TriStar Surface Area and Porosity Analyser is used todetermine pore volume as in the case of surface area measurements andthe same standards are employed.

In the present invention, it has been found that controlling the size ofthe modifier metal moieties is surprisingly advantageous. However, toobtain the greatest benefit it is necessary to control the proximity ofneighbouring modifier metal moieties because the modifier metal moietiesmay otherwise combine with each other and thus increase the size of themodifier metal moiety.

Therefore, according to a fourth aspect of the present invention, thereis provided a method of producing a modified silica support comprisingthe steps of:

providing a silica support having silanol groups;contacting the silica support with a monomeric and/or dimeric modifiermetal compound so that modifier metal is adsorbed onto the surface ofthe silica support through reaction with said silanol groups.

Typically, the modifier metals are selected from zirconium or hafnium.

Preferably, the adsorbed modifier metal cations are sufficiently spacedapart from each other to substantially prevent oligomerisation thereof,more preferably trimerisation thereof with neighbouring modifier metalcations.

Typically, at least 25%, more typically, at least 30%, such as at least35%, more preferably at least 40%, such as at least 45%, most suitablyat least 50%, such as at least 55%, for example at least 60% or 65%, andmost preferably at least 70% such as at least 75% or 80%, moretypically, at least 85%, most typically, at least 90%, especially, atleast 95% of the said modifier metals contacting the silica support inthe contacting step are monomeric or dimeric modifier metals.Accordingly, at least 25%, more typically, at least 30%, such as atleast 35%, more preferably at least 40%, such as at least 45%, mostsuitably at least 50%, such as at least 55%, for example at least 60% or65%, and most preferably at least 70% such as at least 75% or 80%, moretypically, at least 85%, most typically, at least 90%, especially, atleast 95% of the modifier metals adsorbed onto the silica support arepresent in the form of modifier metal moieties having a total of up to 2modifier metal atoms.

According to a further aspect of the present invention there is provideda method of producing a modified silica support according to any of theaspects herein comprising the steps of:

providing a silica support having silanol groups;treating the silica support with monomeric and/or dimeric modifier metalcompounds so that modifier metal is adsorbed onto the surface of thesilica support through reaction with silanol groups, wherein theadsorbed modifier metal atoms are sufficiently spaced apart from eachother to substantially prevent oligomerisation thereof with neighbouringmodifier metal atoms, more preferably, sufficiently spaced apart fromeach other to substantially prevent trimerisation with neighbouringmodifier metal atoms thereof.

Preferably, the spacing apart of the modifier metal atoms is effectedby:

-   -   a) decreasing the concentration of silanol groups on the silica        support and/or    -   b) attaching a non-labile ligand of sufficient size to the        modifier metal prior to treating the silica support.

According to a still further aspect there is provided a method ofproducing a catalyst comprising the steps of:—

-   -   i. providing a silica support with isolated silanol groups and        optionally treating the said support to provide isolated silanol        groups (—SiOH) at a level of <2.5 groups per nm²;    -   ii. contacting the optionally treated silica support with a        monomeric zirconium or hafnium modifier metal compound to effect        adsorption of the said modifier metal onto the support,        typically to at least 25% of the said isolated silanol groups;    -   iii. optionally, removing any solvent or liquid carrier for the        modifier metal compounds;    -   iv. calcining the modified silica for a time and temperature        sufficient to convert the monomeric zirconium or hafnium        compound adsorbed on the surface to an oxide or hydroxide of        zirconium or hafnium;    -   v. treating the said calcined modified silica with a catalytic        alkali metal to impregnate the modified silica with the        catalytic metal to form the catalyst and optionally, calcining        the catalyst.

According to an even further aspect of the present invention there isprovided a method of producing a modified silica support for a catalystcomprising

-   -   the steps of:—    -   i. providing a silica support with isolated silanol groups and        optionally treating the said support to provide isolated silanol        groups (—SiOH) at a level of <2.5 groups per nm²;    -   ii. contacting the optionally treated silica support with a        monomeric zirconium or hafnium modifier metal compound to effect        adsorption of the said modifier metal onto the support,        typically to at least 25% of the said isolated silanol groups;    -   iii. optionally, removing any solvent or liquid carrier for the        modifier metal compounds;    -   iv. optionally calcining the modified support for a time and        temperature sufficient to convert the monomeric zirconium or        hafnium compound adsorbed on the surface to an oxide or        hydroxide of zirconium or hafnium in preparation for catalyst        impregnation.

Preferably, the silanol group concentration is decreased prior totreatment with the modifier metal compounds by calcination treatment,chemical dehydration or other suitable methods.

Preferably, the modifier metal cation source herein is a solution ofcompounds of the said modifier metal so that the compounds are insolution when contacted with the support to effect adsorption onto thesupport.

Typically, the solvent for the said solution is other than water.

Typically, the solvent is an aliphatic alcohol, typically selected fromC1-C6 alkanols such as methanol, ethanol, propanol, isopropanol,butanols, pentanols and hexanols, more typically, methanol, ethanol orpropanols.

Advantageously, the proximity of the adsorbed modifier metal toneighbouring modifier metal cations may be controlled by theconcentration of the said modifier metal in the contacting step and:

-   -   a) the concentration of silanol groups on the silica support        and/or    -   b) the size of any non-labile ligand attached to the modifier        metal cation.

The silanol group concentration on the silica support prior toadsorption is preferably controlled by calcination or other suitablemethods as known to those skilled in the art. Methods of identificationinclude for example L T Zhuravlev, in “Colloids and Surfaces:Physicochemical and Engineering Aspects, vol. 173, pp. 1-38, 2000” whichdescribes four different forms of silanols: isolated silanols, geminalsilanols, vicinal silanols, and internal silanols which can coexist onsilica surfaces. Isolated silanol groups are most preferred. These canbe identified by infrared spectroscopy as a narrow absorption peak at3730-3750 cm⁻¹ whereas other silanols display broad peaks between 3460and 3715 cm⁻¹ (see “The Surface Properties of Silicas, Edited by Andre PLegrand, john Wiley and Sons, 1998 (ISBN 0-471-95332-6) pp. 147-234).

By non-labile ligand is meant a ligand that is co-ordinated to themodifier metal and is not removed by the adsorption of the metal ontothe silica surface. Accordingly, the non-labile ligand is typicallycoordinated to the modifier metal in solution prior to treatment of thesilica surface with modifier metal. For the avoidance of doubt, thenon-labile ligand is typically removed by treatment of the silicasurface following adsorption of the modifier metal.

The size of the non-labile ligand is effective to space the modifiermetals apart to prevent combination thereof.

According to further aspects of the present invention there is providedmethods of producing catalyst or modified silica supports for a catalystor catalysts according to the claims.

The invention extends to a modified silica support according to any ofthe aspects herein, wherein the support comprises isolated silanolgroups (—SiOH) at a level of <2.5 groups per nm². Typically, the supportcomprises isolated silanol groups (—SiOH) at a level of >0.1 and <2.5groups per nm², more preferably, at a level of from 0.2 to 2.2, mostpreferably, at a level of from 0.4 to 2.0 groups per nm².

Still further the invention extends to a catalyst or modified silicasupport according to any aspects herein, wherein the support comprisesthe said zirconium or hafnium modifier metal moieties having a total ofup to 2 modifier metal atoms and/or derived from a monomeric and/ordimeric modifier metal cation source present on the support and presentat a level of <2.5 moieties per nm².

Typically, the support comprises the said zirconium or hafnium modifiermetal moieties at a level of >0.025 and <2.5 groups per nm², morepreferably, at a level of from 0.05 to 1.5, most preferably, at a levelof from 0.1 to 1.0 moieties per nm².

Suitable ligands herein may be non-labile ligands optionally selectedfrom molecules with lone pair containing oxygen or nitrogen atoms ableto form 5 or 6 membered rings with a zirconium or hafnium atom. Examplesinclude diones, diimines, diamines, diols, dicarboxylic acids orderivatives thereof such as esters, or molecules having two differentsuch functional groups and in either case with the respective N or O andN or O atom separated by 2 or 3 atoms to thereby form the 5 or 6membered ring. Examples include pentane-2,4-dione, esters of3-oxobutanoic acid with aliphatic alcohols containing 1-4 carbon atomssuch as ethyl 3-oxobutanoate, propyl 3-oxobutanoate, isopropyl3-oxobutanoate, n-butyl 3-oxobutanoate, t-butyl 3-oxobutanoate,heptane-3,5-dione, 2,2,6,6-Tetramethyl-3,5-heptanedione, 1,2-ethanediol,1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,2-butanediol,1,2-diaminoethane, ethanolamine, 1,2-diamino-1,1,2,2-tetracarboxylate,2,3-dihydroxy-1,4-butanedioate, 2,4-dihydroxy-1,5-pentanedioate, saltsof 1,2-dihydroxylbenzene-3-5-disulphonate, diethylenetriaminepentaaceticacid, nitrolotriacetic acid, N-hydroxyethylethylenediaminetriaceticacid, N-hydroxyethyliminodiacetic acid, N,N-dihydroxyethylglycine,oxalic acid and its salts. Pentane-2,4-dione, heptane-3,5-dione,2,2,6,6-Tetramethyl-3,5-heptanedione, ethyl 3-oxobutanoate and t-butyl3-oxobutanoate are most preferred. The smaller bidentate ligands having,for example less than 10 carbon and/or hetero atoms in total enablesmall complexes to be formed which can allow higher concentrations to bedeposited on the surface of the silica compared to larger ligands.Accordingly, the modifier metal cation source herein may be in the formof complexes of zirconium and/or hafnium with such smaller ligands,preferably, with at least one such ligand. Such compounds may includelabile ligands such as solvent ligands, for example in alcohol solvent,alkoxide ligands such as ethoxide or propoxide etc.

The concentration of preferably isolated silanol groups determines themaximum number of sites for modifier metal adsorption. By controllingthis concentration, the proximity of the adsorbed modifier metal can beeffectively determined because the distribution of silanol sites willgenerally be homogeneous. The silanol concentration for the productionof a modified silica support according to the present inventions may bebelow 2.5 groups per nm², more typically, less than 1.5 groups per nm²,most typically, less than 0.8 groups per nm². Suitable ranges for thesilanol concentration for production of a modified silica supports maybe 0.1-2.5 silanol groups per nm², more preferably 0.15-1.0 silanolgroups per nm², most preferably 0.2-0.7 silanol groups per nm².

The concentration of the modifier metal, generally in the form of acation should be set at a level that prevents the significant formationof bilayers etc. on the surface of the support which would lead tomodifier metal to metal interaction. In addition, filling in of gaps inthe initial monolayer that could result in weak adsorption of themodifier metal away from silanol sites should also be avoided to preventinteraction with neighbouring strongly adsorbed modifier metals. Typicalconcentration ranges for the modifier metals of the invention may be asset out herein.

Typically, at least 30%, such as at least 35%, more preferably at least40%, such as at least 45%, most suitably at least 50%, such as at least55%, for example at least 60% or 65%, and most preferably at least 70%such as at least 75% or 80%, more typically, at least 85%, mosttypically, at least 90%, especially, at least 95% of the modifier metalin the modifier metal compounds are dimeric and/or monomeric modifiermetal compounds when the source thereof is contacted with the support toeffect adsorption of the said compounds onto the support, moretypically, monomeric.

According to a further aspect of the present invention there is provideda method of producing a catalyst comprising

a modified silica support,the modified silica support comprising a modifier metal;

-   -   and a catalytic metal on the modified silica support,    -   wherein the modifier metal is selected from one or more of        zirconium and/or hafnium,    -   characterised in that at least a proportion, typically, at least        25%, of the said modifier metal is present in the form of        monomeric modifier metal moieties    -   the said method comprising    -   the steps of:—    -   treating the silica support to provide isolated silanol groups        (—SiOH) at a level <2.5 groups per nm²;    -   reacting the treated support with monomeric zirconium or hafnium        monomeric modifier metal compounds to effect bonding thereof to        at least 25% of the said isolated silanol groups;    -   optionally, removing any solvent or liquid carrier;    -   calcining the modified silica for a time and temperature        sufficient to convert the monomeric zirconium or hafnium        compound adsorbed on the surface to an oxide or hydroxide of        zirconium or hafnium;    -   treating the said calcined modified silica with a catalytic        alkali metal to impregnate the modified silica with the        catalytic metal.

Advantageously, by providing a smaller number of isolated silanol sitesand by bonding monomeric zirconium or hafnium species to these sites acatalyst support is provided that leads to improved selectivity of thecatalyst, lower sintering rate and better ageing of catalyst.

A suitable method of treating the silica to provide the isolated silanolgroups at the level specified is by calcination. However, othertechniques such as hydrothermal treatment or chemical dehydration arealso possible. U.S. Pat. No. 5,583,085 teaches chemical dehydration ofsilica with dimethyl carbonate or ethylene dicarbonate in the presenceof an amine base. U.S. Pat. No. 4,357,451 and U.S. Pat. No. 4,308,172teach chemical dehydration by chlorination with SOCl₂ followed bydechlorination with H₂ or ROH followed by oxygen in a dry atmosphere.Chemical dehydration may provide up to 100% removal of silanols againsta minimum of 0.7/nm² by thermal treatment. Thus, in some instances,chemical dehydration may provide more scope for silanol group control.

The term isolated silanol (also known as single silanol) is well knownin the art and distinguishes the groups from vicinal or geminal orinternal silanols. Suitable methods for determining the incidence ofisolated silanols include surface sensitive infrared spectroscopy and ¹HNMR or ³¹Si NMR.

According to a fifth aspect of the present invention there is provided amethod of producing a catalyst according to any previous aspects of thepresent invention, comprising the steps of: forming a modified silicaaccording to any previous aspect, and contacting the modified silicasupport with a solution containing a catalytic metal to impregnate themodified silica with the catalytic metal.

Preferably, the silica support is dried or calcined prior to treatmentwith the modifier metal cation source. The modified silica formed mayirrespective of whether previously dried or calcined be dried orcalcined prior to addition of the catalytic metal.

The silica may be in the form of a gel prior to treatment with themodifier metal. The gel may be in the form of a hydrogel, a xerogel oran aerogel at the commencement of modification.

The silica support may be a xerogel, hydrogel or aerogel. Preferably,the silica support is a xerogel.

The silica support may be treated by the metal cation source by any ofthe various techniques known to those skilled in the art of supportformation. The silica support may be contacted with the metal cationsource in such a manner so as to disperse modifier metal throughout thesilica support. Typically, the zirconium and/or hafnium may behomogeneously dispersed throughout the silica support. Preferably,modifier metal is dispersed through the silica support by adsorption.

By the term “adsorption” or the like in relation to the modifier metalas used herein is meant the incorporation of modifier metal onto thesilica support surface by the interaction of the metal cation sourcewith the silica support, typically by chemisorption. Typically, additionof the modifier to the silica support involves the steps of: adsorptionof the metal cation source onto the silica support to form an organicmetal complex and calcination of the complex to convert the organicmetal complexes to metal oxide moieties. Typically, there is therefore ahomogeneous dispersion of modifier metal throughout the silica support.Typically, zirconium and/or hafnium is dispersed throughout the silicasupport.

Examples of suitable metal cation sources herein include organiccomplexes such as zirconium (pentane-2,4-dione)₄, zirconium(ethyl3-oxobutanoate)₄, zirconium(heptane-3,5-dione)₄,zirconium(2,2,6,6-tetramethylheptane-3,5-dione)₄,zirconium(propoxide)(pentane-2-3-dione)₃,zirconium(propoxide)₃(2,2,6,6-tetramethyl-3,5-heptanedione)(zirconium(Ot-butyl)₃(t-butyl 3-oxobutanoate),zirconium(Ot-butyl)₂(t-butyl 3-oxobutanoate)₂ and metal salts such aszirconium perchlorate, zirconium oxynitrate and zirconium oxychlorideTypically, the metal cation source is provided as an organic complex.

Typically, the modifier metal is contacted with the silica support insolution

Preferably, the metal cation source is provided in any solvent in whichthe metal cation source is soluble. Examples of suitable solvent includewater or alcohols. Preferred solvents are alcohols such as methanol,ethanol, propanol, isopropanol, butanols, pentanols and hexanols.

Preferably, the metal cation source is added to the silica as a metalsalt in such alcoholic solution.

In one embodiment, the metal cation source is provided as a solution ofone or more of zirconium(IV)acetylacetonate(zirconium,tetrakis(2,4-pentanedionato-O,O′)),zirconium(heptane-3,5-dione)₄,zirconium(2,2,6,6-tetramethyl-3,5-heptanedione)₄, zirconium(IV) ethyl3-oxobutanoate, zirconium(IV) t-butyl 3-oxobutanoate, or zirconium(IV)i-propyl 3-oxobutanoate in one of methanol, ethanol, isopropanol,propanol, butanol, isobutanol, or 2-butanol.

Preferably, after adsorption of the modifier metal onto the silicasupport, the solvent is removed by evaporation.

Optionally, the modified silica support is calcined to remove anyligands or other organics from the modified support.

It will be understood by a skilled person that the catalytic metal maybe added to the modified silica by any suitable means. Typically, inorder to produce the modified silica catalyst, the modified silica iscontacted with a catalytic metal.

Typically, in order to produce the catalyst, the modified silica supportis contacted with an acidic, neutral or alkaline aqueous solutioncontaining a catalytic metal such as caesium, in the form of a salt of acatalytic metal and a base. Alternatively, the support can be contactedwith a water miscible solution of the catalytic metal salt in an organicsolvent. Preferred solvents are alcohols such as methanol, ethanol,propanol and isopropanol, preferably methanol. The most preferredsolvent is methanol. Most preferably, the catalytic metal is added as asalt solution in methanol. Low levels of water, typically up to 20 vol %can be contained in the solutions.

Typically, the conditions of temperature, contact time and pH duringthis stage of the catalyst production process are such as to allow forimpregnation of the modified silica support with the catalytic metal toform a modified silica supported catalyst.

Typical conditions of temperature for this step are between 5-95° C.,more typically 10-80° C. and most typically between 20-70° C. Thetemperature for this step may be at least 5° C., more typically at least10° C., most typically, at least 20° C.

Typical contact times between the modified support and the catalyticmetal containing solution for this step may be between 0.05-48 hours,more typically between 0.1-24 hours, most typically between 0.5-18hours. The contact time may be at least 0.05 hours, more typically atleast 0.1 hours, most typically at least 0.5 hours.

The concentration of the catalytic metal salt solution for this step isdependent on a large number of factors including the solubility limit ofthe catalytic metal compound, the porosity of the modified silicasupport, the desired loading of the catalytic metal on the support andthe method of addition, including the amount of liquid used toimpregnate the support, the pH and the choice of the catalytic metalcompound. The concentration in solution is best determined byexperiment.

Suitable salts of catalytic metals for incorporation of the catalyticmetal generally may be selected from one or more of the group consistingof formate, acetate, propionate, hydrogen carbonate, chloride, nitrate,hydroxide and carbonate, more typically, hydroxide, acetate or carbonateand most typically hydroxide and/or carbonate. The pH can be controlledduring the impregnation by addition of ammonia with the metal compoundor by using an appropriate catalytic metal compound such as the formate,carbonate, acetate or hydroxide, more preferably, the hydroxide orcarbonate, in all cases either alone, in combination, or together withan appropriate carboxylic acid. The control of the pH in the preferredranges is most important at the end of the impregnation to effectsatisfactory adsorption. Most typically, these salts may be incorporatedusing an alkaline solution of the salt. If the salt is not itselfalkaline then a suitable base such as ammonium hydroxide may be added.As hydroxide salts are basic in nature, mixtures of one or more of theabove salts with the hydroxide salt of the particular catalytic metalsuch as caesium may conveniently be prepared.

It will be understood by the skilled person that a catalytic metal ofthe present invention may be added to the modified silica support by anysuitable means. The catalyst may be fixed, typically by calcination,onto the support after deposition of the compound onto the supportoptionally using a suitable aqueous salt and subsequent drying of thesurface coated support.

Generally, drying of the modified silica support is achieved byappropriate methods known to the skilled person such as in a drying unitor oven.

Typically, the catalyst contains between 0.01-25% w/w water, moretypically 0.1-15% w/w water and most typically between 0.5%-5.0 w/wwater.

Optionally, the modified silica supported catalyst containing catalyticmetal may be dried or calcined, the process of calcination is well knownto those skilled in the art.

In some cases, it may be necessary to calcine the support formed fromthe modification stage at 200-1000° C., more typically, 300-800° C.,most typically, 350-600° C. prior to addition of the catalytic metal. Inpreferred calcinations of the support formed from the modificationstage, the temperature is at least 375° C., such as 400° C. or 450° C.The calcination atmosphere should typically contain some oxygen,suitably 1-30% oxygen and most suitably 2-20% oxygen to effect removalof the organic residues as carbon dioxide and water. The calcinationtime may typically be between 0.01 and 100 hours, suitably 0.5-40 hours,most suitably 1-24 hours. The calcined support such as xerogel materialshould be cooled to the appropriate temperature for impregnation.Addition of the catalytically active metal can be carried out by methodsdescribed for the uncalcined material or can be by any other normalmethod used to impregnate catalyst supports, such as xerogel supports,such as using a solvent other than water such as an alcohol, suitablymethanol, ethanol, propanol or isopropanol or using the incipientwetness method where only sufficient solution is added to the xerogelsupports to fill the pores of the xerogel support. In this case, theconcentration of the catalytically active metal may be calculated so asto introduce the target amount of catalytically active metal to thexerogel support material rather than providing an excess of solution oflower concentration by the method described earlier. The addition of thecatalytically active metal may utilise any preferred methodology knownin the art. The calcining technique is particularly advantageous wherean organic complex is used as the source of the zirconium and/or hafniumas it may be necessary to modify the subsequent catalyst preparationprocedure so as to remove at least a fraction of the organic complexingsalt prior to impregnation with caesium. Advantageously, it has beenfound that the catalytic metal:modifier metal ratio and therefore thecatalytic metal required is lowered by the calcination of the modifiedsupport. This was unexpected and provides a further improvement to theinvention.

According to a sixth aspect of the present invention there is provided amethod of producing an ethylenically unsaturated carboxylic acid orester, typically, an α, β ethylenically unsaturated carboxylic acid orester, comprising the steps of contacting formaldehyde or a suitablesource thereof with a carboxylic acid or ester in the presence ofcatalyst and optionally in the presence of an alcohol, wherein thecatalyst is according to the first or any of the other aspects of thepresent invention defined herein.

Advantageously, it has also been found that catalysts comprisingmodified silicas as defined herein and containing a catalytic metal areremarkably effective catalysts for the production of α, β ethylenicallyunsaturated carboxylic acid or esters by condensation of thecorresponding acid or ester with a methylene source such as formaldehydehaving reduced sintering of the catalyst surface, improved selectivityand providing high catalyst surface area. In particular enhancedproperties are found when using monomeric and/or dimeric modifier metalmoieties and/or when the modified silica support is calcined prior totreatment with the catalytic metal. Furthermore, the use of certainmetal complexes to incorporate the modifier metal onto the support byadsorption provides a convenient source of monomeric and/or dimericmodifier metal moieties. Such a source also allows control of the natureof the modifier metal and provides a more uniform distribution ofmodifier metal moieties.

By the term “a suitable source thereof” in relation to formaldehyde ofthe fourth aspect of the present invention is meant that the freeformaldehyde may either form in situ from the source under reactionconditions or that the source may act as the equivalent of freeformaldehyde under reaction conditions, for example it may form the samereactive intermediate as formaldehyde so that the equivalent reactiontakes place.

A suitable source of formaldehyde may be a compound of formula (I):

wherein R⁵ and R⁶ are independently selected from C₁-C₁₂ hydrocarbons orH, X is O, n is an integer from 1 to 100, and m is 1.

Typically, R⁵ and R⁶ are independently selected from C₁-C₁₂ alkyl,alkenyl or aryl as defined herein, or H, more suitably, C₁-C₁₀ alkyl, orH, most suitably, C₁-C₆ alkyl or H, especially, methyl or H. Typically,n is an integer from 1 to 10, more suitably 1 to 5, especially, 1-3.

However, other sources of formaldehyde may be used including trioxane.

Therefore, a suitable source of formaldehyde also includes anyequilibrium composition which may provide a source of formaldehyde.Examples of such include but are not restricted to dimethoxymethane,trioxane, polyoxymethylenes R¹—O—(CH₂—O)_(i)—R² wherein R¹ and/or R² arealkyl groups or hydrogen, i=1 to 100, paraformaldehyde, formalin(formaldehyde, methanol, water) and other equilibrium compositions suchas a mixture of formaldehyde, methanol and methyl propionate.

Polyoxymethylenes are higher formals or hemiformals of formaldehyde andmethanol CH₃—O—(CH₂—O)_(i)—CH₃ (“formal-i”) or CH₃—O—(CH₂—O)_(i)—H(“hemiformal-i”), wherein i=1 to 100, suitably, 1-5, especially 1-3, orother polyoxymethylenes with at least one non methyl terminal group.Therefore, the source of formaldehyde may also be a polyoxymethylene offormula R³¹—O—(CH2-O—)_(i)R³², where R³¹ and R³² may be the same ordifferent groups and at least one is selected from a C₁-C₁₀ alkyl group,for instance R³¹=isobutyl and R³²=methyl.

Generally, the suitable source of formaldehyde is selected fromdimethoxymethane, lower hemiformals of formaldehyde and methanol,CH₃—O—(CH₂—O)_(i)—H where i=1-3, formalin or a mixture comprisingformaldehyde, methanol and methyl propionate.

Typically, by the term formalin is meant a mixture offormaldehyde:methanol:water in the ratio 25 to 65%:0.01 to 25%:25 to 70%by weight. More typically, by the term formalin is meant a mixture offormaldehyde:methanol:water in the ratio 30 to 60%:0.03 to 20%:35 to 60%by weight. Most typically, by the term formalin is meant a mixture offormaldehyde:methanol:water in the ratio 35 to 55%:0.05 to 18%:42 to 53%by weight.

Typically, the mixture comprising formaldehyde, methanol and methylpropionate contains less than 5% water by weight. More suitably, themixture comprising formaldehyde, methanol and methyl propionate containsless than 1% water by weight. Most suitably, the mixture comprisingformaldehyde, methanol and methyl propionate contains 0.1 to 0.5% waterby weight.

According to a seventh aspect of the present invention, there isprovided a process for preparing an ethylenically unsaturated acid orester comprising contacting an alkanoic acid or ester of the formulaR¹—CH₂—COOR³, with formaldehyde or a suitable source of formaldehyde offormula (I) as defined below:

where R5 is methyl and R6 is H;

X is O;

m is 1;and n is any value between 1 and 20 or any mixture of these;in the presence of a catalyst according to any aspect of the presentinvention, and optionally in the presence of an alkanol; wherein R1 ishydrogen or an alkyl group with 1 to 12, more Suitably, 1 to 8, mostsuitably, 1 to 4 carbon atoms and R3 may also be independently, hydrogenor an alkyl group with 1 to 12, more suitably, 1 to 8, most suitably, 1to 4 carbon atoms.

Therefore, the present inventors have discovered that having zirconiumand/or hafnium in the form of metal oxide moieties according to thepresent invention enables surprising improvement in selectivity for thecondensation of methylene sources such as formaldehyde with a carboxylicacid or alkyl ester such as methyl propionate to form ethylenicallyunsaturated carboxylic acids. In addition, the rate of sintering of thecatalyst surface during the condensation reaction is significantly andsurprisingly reduced.

Accordingly, one particular process for which the catalysts of thepresent invention have been found to be particularly advantageous is thecondensation of formaldehyde with methyl propionate in the presence ofmethanol to produce MMA.

In the case of production of MMA, the catalyst is typically contactedwith a mixture comprising formaldehyde, methanol and methyl propionate.

The process of the sixth or seventh aspect of the invention isparticularly suitable for the production of acrylic and alkacrylic acidsand their alkyl esters, and also methylene substituted lactones.Suitable methylene substituted lactones include 2-methylenevalerolactone and 2-methylene butyrolactone from valerolactone andbutyrolactone respectively. Suitable, (alk)acrylic acids and theiresters are (C₀₋₈alk)acrylic acid or alkyl (C₀₋₈alk)acrylates, typicallyfrom the reaction of the corresponding alkanoic acid or ester thereofwith a methylene source such as formaldehyde in the presence of thecatalyst, suitably the production of methacrylic acid, acrylic acid,methyl methacrylate, ethyl acrylate or butyl acrylate, more suitably,methacrylic acid or especially methyl methacrylate (MMA) from propanoicacid or methyl propionate respectively. Accordingly, in the productionof methyl methacrylate or methacrylic acid, the preferred ester or acidof formula R¹—CH₂—COOR³ is methyl propionate or propionic acidrespectively and the preferred alkanol is therefore methanol. However,it will be appreciated that in the production of other ethylenicallyunsaturated acids or esters, the preferred alkanols or acids will bedifferent.

The reaction of the present invention may be a batch or continuousreaction.

Typical conditions of temperature and gauge pressure in the process ofthe sixth or seventh aspect of the invention are between 100° C. and400° C., more preferably, 200° C. and 375° C., most preferably, 275° C.and 360° C.; and/or between 0.001 MPa and 1 MPa, more preferably between0.03 MPa and 0.5 MPa, most preferably between 0.03 MPa and 0.3 MPa.Typical residence times for the reactants in the presence of thecatalyst are between 0.1 and 300 secs, more preferably between, 1-100secs, most preferably between 2-50 secs, especially, 3-30 secs.

The amount of catalyst used in the process of production of product inthe present invention is not necessarily critical and will be determinedby the practicalities of the process in which it is employed. However,the amount of catalyst will generally be chosen to effect the optimumselectivity and yield of product and an acceptable temperature ofoperation. Nevertheless, the skilled person will appreciate that theminimum amount of catalyst should be sufficient to bring about effectivecatalyst surface contact of the reactants. In addition, the skilledperson would appreciate that there would not really be an upper limit tothe amount of catalyst relative to the reactants but that in practicethis may be governed again by the contact time required and/or economicconsiderations.

The relative amount of reagents in the process of the sixth or seventhaspect of the invention can vary within wide limits but generally themole ratio of formaldehyde or suitable source thereof to the carboxylicacid or ester is within the range of 20:1 to 1:20, more suitably, 5:1 to1:15. The most preferred ratio will depend on the form of theformaldehyde and the ability of the catalyst to liberate formaldehydefrom the formaldehydic species. Thus highly reactive formaldehydicsubstances where one or both of R³¹ and R³² in R³¹O—(CH₂—O)_(i)R³² is Hrequire relatively low ratios, typically, in this case, the mole ratioof formaldehyde or suitable source thereof to the carboxylic acid orester is within the range of 1:1 to 1:9. Where neither of R³¹ and R³² isH, as for instance in CH₃O—CH₂—OCH₃, or in trioxane higher ratios aremost preferred, typically, 6:1 to 1:3.

As mentioned above, due to the source of formaldehyde, water may also bepresent in the reaction mixture. Depending on the source offormaldehyde, it may be necessary to remove some or all of the watertherefrom prior to catalysis. Maintaining lower levels of water thanthat in the source of formaldehyde may be advantageous to the catalyticefficiency and/or subsequent purification of the products. Water at lessthan 10 mole % in the reactor is preferred, more suitably, less than 5mole %, most suitably, less than 2 mole %.

The molar ratio of alcohol to the acid or ester is typically within therange 20:1 to 1:20, preferably 10:1 to 1:10, most preferably 5:1 to 1:5,for example 1:1.5. However, the most preferred ratio will depend on theamount of water fed to the catalyst in the reactants plus the amountproduced by the reaction, so that the preferred molar ratio of thealcohol to the total water in the reaction will be at least 1:1 and morepreferably at least 2:1.

The reagents of the sixth or seventh aspect may be fed to the reactorindependently or after prior mixing and the process of reaction may becontinuous or batch. Typically, however, a continuous process is used.

Typically, the method of the sixth or seventh aspect of the presentinvention is carried out when reactants are in the gaseous phase.

In a still further aspect, the invention extends to the process ofproducing an ethylenically unsaturated carboxylic acid or esteraccording to any of the relevant aspects herein comprising the steps offirst producing a catalyst according to any of the relevant aspectsherein.

Definitions

The term “alkyl” when used herein, means, unless otherwise specified, C₁to C₁₂ alkyl and includes methyl, ethyl, ethenyl, propyl, propenylbutyl, butenyl, pentyl, pentenyl, hexyl, hexenyl and heptyl groups,typically, the alkyl groups are selected from methyl, ethyl, propyl,butyl, pentyl and hexyl, more typically, methyl. Unless otherwisespecified, alkyl groups may, when there is a sufficient number of carbonatoms, be linear or branched, be cyclic, acyclic or part cyclic/acyclic,be unsubstituted, substituted or terminated by one or more substituentsselected from halo, cyano, nitro, —OR¹⁹, —OC(O)R²⁰, —C(O)R²¹, —C(O)OR²²,—NR²³R²⁴, C(O)NR²⁵R²⁶, —SR²⁹, —C(O)SR³⁰, —C(S)NR²⁷R²⁸, unsubstituted orsubstituted aryl, or unsubstituted or substituted Het, wherein R¹⁹ toR³⁰ here and generally herein each independently represent hydrogen,halo, unsubstituted or substituted aryl or unsubstituted or substitutedalkyl, or, in the case of R²¹, halo, nitro, cyano and amino and/or beinterrupted by one or more (typically less than 4) oxygen, sulphur,silicon atoms, or by silano or dialkylsilcon groups, or mixturesthereof. Typically, the alkyl groups are unsubstituted, typically,linear and typically, saturated.

The term “alkenyl” should be understood as “alkyl” above except at leastone carbon-carbon bond therein is unsaturated and accordingly the termrelates to C₂ to C₁₂ alkenyl groups.

The term “alk” or the like should, in the absence of information to thecontrary, be taken to be in accordance with the above definition of“alkyl” except “C₀ alk” means non-substituted with an alkyl.

The term “aryl” when used herein includes five-to-ten-membered,typically five to eight membered, carbocyclic aromatic or pseudoaromatic groups, such as phenyl, cyclopentadienyl and indenyl anions andnaphthyl, which groups may be unsubstituted or substituted with one ormore substituents selected from unsubstituted or substituted aryl, alkyl(which group may itself be unsubstituted or substituted or terminated asdefined herein), Het (which group may itself be unsubstituted orsubstituted or terminated as defined herein), halo, cyano, nitro, OR¹⁹,OC(O)R²⁰, C(O)R²¹, C(O)OR²², NR²³R²⁴, C(O)NR²⁵R²⁶, SR²⁹, C(O)SR³⁰ orC(S)NR²⁷R²⁸ wherein R¹⁹ to R³⁰ each independently represent hydrogen,unsubstituted or substituted aryl or alkyl (which alkyl group may itselfbe unsubstituted or substituted or terminated as defined herein), or, inthe case of R²¹, halo, nitro, cyano or amino.

The term “halo” when used herein means a chloro, bromo, iodo or fluorogroup, typically, chloro or fluoro.

The term “Het”, when used herein, includes four- to twelve-membered,typically four- to ten-membered ring systems, which rings contain one ormore heteroatoms selected from nitrogen, oxygen, sulfur and mixturesthereof, and which rings contain no, one or more double bonds or may benon-aromatic, partly aromatic or wholly aromatic in character. The ringsystems may be monocyclic, bicyclic or fused. Each “Het” groupidentified herein may be unsubstituted or substituted by one or moresubstituents selected from halo, cyano, nitro, oxo, alkyl (which alkylgroup may itself be unsubstituted or substituted or terminated asdefined herein) —OR¹⁹, —OC(O)R²⁰, —c(O)R²¹, —C(O)OR²², —N(R²³)R²⁴,—C(O)N(R²⁵)R²⁶, —SR²⁹, —C(O)SR³⁹ or —C(S)N(R²⁷)R²⁸ wherein R¹⁹ to R³⁰each independently represent hydrogen, unsubstituted or substituted arylor alkyl (which alkyl group itself may be unsubstituted or substitutedor terminated as defined herein) or, in the case of R²¹, halo, nitro,amino or cyano. The term “Het” thus includes groups such as optionallysubstituted azetidinyl, pyrrolidinyl, imidazolyl, indolyl, furanyl,oxazolyl, isoxazolyl, oxadiazolyl, thiazolyl, thiadiazolyl, triazolyl,oxatriazolyl, thiatriazolyl, pyridazinyl, morpholinyl, pyrimidinyl,pyrazinyl, quinolinyl, isoquinolinyl, piperidinyl, pyrazolyl andpiperazinyl. Substitution at Het may be at a carbon atom of the Het ringor, where appropriate, at one or more of the heteroatoms.

“Het” groups may also be in the form of an N oxide.

Suitable optional alcohols for use in the catalysed reaction of thefourth and fifth aspects of the present invention may be selected from:a C₁-C₃₀ alkanol, including aryl alcohols, which may be optionallysubstituted with one or more substituents selected from alkyl, aryl,Het, halo, cyano, nitro, OR¹⁹, OC(O)R²⁰, C(O)R²¹, C(O)OR²², NR²³R²⁴,C(O)NR²⁵R²⁶, C(S)NR²⁷R²⁸, SR²⁹ or C(O)SR³⁰ as defined herein. Highlypreferred alkanols are C₁-C₈ alkanols such as methanol, ethanol,propanol, iso-propanol, iso-butanol, t-butyl alcohol, phenol, n-butanoland chlorocapryl alcohol, especially, methanol. Although themonoalkanols are most preferred, poly-alkanols, typically, selected fromdi-octa ols such as diols, triols, tetra-ols and sugars may also beutilised. Typically, such polyalkanols are selected from 1,2-ethanediol, 1,3-propanediol, glycerol, 1,2,4 butanetriol,2-(hydroxymethyl)-1,3-propanediol, 1,2,6 trihydroxyhexane,pentaerythritol, 1,1,1 tri(hydroxymethyl)ethane, nannose, sorbase,galactose and other sugars. Preferred sugars include sucrose, fructoseand glucose. Especially preferred alkanols are methanol and ethanol. Themost preferred alkanol is methanol. The amount of alcohol is notcritical. Generally, amounts are used in excess of the amount ofsubstrate to be esterified. Thus the alcohol may serve as the reactionsolvent as well, although, if desired, separate or further solvents mayalso be used.

The term ageing is described in, for example, patent application WO2009/003722. The general principles of ageing are described in TheChemistry of Silica: Solubility, Polymerisation, Colloid and SurfaceProperties and Biochemistry of Silica: by Ralph K Iler, 1979, John Wileyand Sons Inc., ISBN 0-471-02404-X, pages 358-364. If this stage isundertaken, the hydrogel is then washed again to remove any materialsused in the ageing process and to bring the solution to the correct pHfor addition of catalytically active metal which depends on the choiceof salt for the catalytically active metal.

Although the metal, metal oxide and metal oxide moieties of any aspectof the present invention or any preferred or optional feature thereofmay be zirconium or hafnium and zirconia or hafnia respectively, theyare typically, zirconium and zirconia and moieties of zirconia.

The term “gel” as used herein is also known to the skilled person but incase of doubt may be taken to be a solid network in which a fluid isdispersed. Generally, the gel is a polymer network in which fluid isdispersed. A co-gel is a term used to indicate that more than oneoriginal chemical compound/moiety is incorporated into the polymericnetwork, usually silica and a metal oxide or salt such as zirconia.Accordingly, co-gelation herein means the formation of a co-gel.

A gel is thus a sol that has set. A Hydrogel is thus a gel as definedherein where the fluid is water. A Xerogel is a gel that has been driedto remove the fluid. An Aerogel is a gel in which the fluid is replacedby a gas and therefore is not subject to the same shrinkage as aXerogel.

The term commencement herein means the beginning of the formation of themodified silica.

The term “moieties” as used herein in relation to the metal is used torefer to the form of the modifier metal on the modified support.Although, the modifier metal generally forms part of a network, themodifier metal will be in the form of discrete residues on the silicasubstrate. Reference to a total of up to two metal atoms or the likeshould be taken to refer to the monomeric and/or the dimeric form of theresidue thereof. Suitably in the aspects of the present inventionherein, it has been found to be advantageous to have the moieties in theform of a monomeric residue. Accordingly, the term up to 2 modifiermetal atoms or the like herein means a total of 1 and/or 2 modifiermetal atoms. Herein, 1 is preferred to 2 modifier metal atoms,especially preferred is a total of 1 and/or 2 zirconium atoms in thesaid moieties, most especially 1 zirconium atom in the moieties.

The term monomeric or dimeric means having monomer like or dimer likeform or in the case of residues on the silica i.e. having the form of amonomer or dimer residue.

% of the modifier metal has no units herein because it refers to numberof metal atoms per total number of such atoms. It will be appreciatedthat the moieties may take the form of non-monomeric or non-dimericclusters but that these clusters are still made up of modifier metalatoms.

Embodiments of the invention will now be defined by reference to theaccompanying examples and figures in which:

FIG. 1 shows the HRTEM image for the Zr modified silica example 5;

FIG. 2 shows the HRTEM image for the Zr modified silica example 7;

FIG. 3 shows the HRTEM image for the Zr modified silica example 14;

FIG. 4 shows the HRTEM image for the Zr modified silica example 15;

FIG. 5 shows the HRTEM image for the Zr modified silica example 17; and

FIG. 6 shows the HRTEM image for the Zr modified silica example 18;

FIG. 7 shows the MMA+MAA selectivity (%) vs. catalyst activity for thecatalysts prepared in Example 20 to Example 74;

FIG. 8 shows the catalyst selectivity for mixed monomer/trimer catalystsprepared in Example 75 to Example 79; and

FIG. 9 shows the catalyst sintering constants as determined by theadvanced ageing test described in Example 81.

EXPERIMENTAL Silica Support Description Example 1

Fuji Silysia CARiACT Q10 silica (Q10) was dried in a laboratory oven at160° C. for 16 hours, after which it was removed from the oven andcooled to room temperature in a sealed flask stored in a desiccator.This silica had a surface area of 333 m²/g, a pore volume of 1.0 ml/g,and an average pore diameter of 10 nm as determined by nitrogenadsorption/desorption isotherm analysis (Micromeretics Tristar II). Asilanol number of 0.8 OH/nm² was found through TGA analysis. This silicais primarily composed of spherical silica beads in the diameter range of2-4 mm.

Example 2

Fuji Silysia CARiACT Q30 silica (Q30) was calcined in a tubular furnaceat 900° C. for 5 hours with a heating ramp rate of 5° C./min under aflow of nitrogen gas. It was then cooled down to room temperature andstored in a sealed flask in a desiccator. This silica had a surface areaof 112 m²/g, a pore volume of 1.0 ml/g, an average pore diameter of 30nm and is primarily composed of spherical silica beads in the diameterrange of 2-4 mm.

Zr Modification of Silica Supports Example 3 (0.92 wt % Zr, Monomeric Zron Q10)

0.542 g of, Zr(acac)₄ (97%, Sigma Aldrich) was dissolved in 11 ml ofMeOH (99% Sigma Aldrich). In a separate flask 10 g of the silica fromExample 1 was weighed off. The weighed off silica was then added to theZr(acac)₄ solution with agitation. Agitation was continued until all ofthe Zr(acac)₄ solution had been taken up into the pore volume of thesilica. Once pore filling had been completed the Zr-modified silica wasleft for 16 hours in a sealed flask with periodic agitation. After thistime the extra-porous solution was removed by filtration. This wasfollowed by a drying step where the intra-porous organic solvent wasremoved by passing a flow of nitrogen gas over the wet Zr-modifiedsilica at room temperature. Alternatively, the intra-porous solvent wasremoved on a rotary evaporator at reduced pressure. Once all of thesolvent had been removed the Zr-modified silica support was calcined ina tubular furnace at 500° C. under a flow of air (1 l/min) with aheating ramp rate of 5° C./min and a final hold of 5 hours. Upon coolingthis yielded the Zr grafted silica support with a 100% Zr usageefficiency. The Zr load (wt %) on the Zr-modified support was determinedvia powder Energy Dispersive X-Ray Fluorescence analysis (OxfordInstruments X-Supreme8000).

Example 4 (1.5 wt % Zr, Monomeric Zr on Q10)

A support modification as described in Example 3 was performed exceptthat 0.874 g of Zr(acac)₄ was used.

Example 5 (2.3 wt % Zr, Monomeric Zr on Q10)

A support modification as described in Example 3 was performed exceptthat 1.38 g of Zr(acac)₄ was used and 20 ml of 1-PrOH (99% SigmaAldrich) was used instead of MeOH. Additionally, agitation was continuedthroughout the 16 h ageing step prior to solvent removal. This resultedin a 90% Zr usage efficiency.

Example 6 (2.7 wt % Zr, Monomeric Zr on Q10)

A support modification as described in Example 5 was performed exceptthat 1.67 g of Zr(acac)₄ was used and 20 ml of MeOH (99% Sigma Aldrich)was used instead of 1-PrOH. This resulted in an 89% Zr usage efficiency.

Example 7 (4.2 wt % Zr, Monomeric Zr on Q10)

A support modification as described in Example 5 was performed exceptthat 2.56 g of Zr(acac)₄ was used and 20 ml of toluene (99% SigmaAldrich) was used instead of 1-PrOH. This resulted in a 93% Zr usageefficiency.

Example 8 (0.7 wt % Zr, Monomeric Zr on Q30)

A support modification as described in Example 6 was performed exceptthat 0.43 g of Zr(acac)₄ was used and silica from Example 2 was used.This resulted in a 93% Zr usage efficiency.

Example 9 (1.1 wt % Zr, Monomeric Zr on Q10)

A support modification as described in Example 5 was performed exceptthat 2.15 g of Zr(thd)₄ was used and 20 ml of MeOH was used instead of1-PrOH. This resulted in a 47% Zr usage efficiency.

Example 10 (2.2 wt % Zr, Monomeric Zr on Q10)

A support modification as described in Example 9 was performed except 20ml of toluene was used instead of MeOH. This resulted in a 93% Zr usageefficiency.

Example 11 (3.9 wt % Zr, Monomeric Zr on Q10)

A support modification as described in Example 5 was performed exceptthat 3.19 g of Zr(EtOAc)₄ was used and 20 ml of heptane (99% SigmaAldrich) was used instead of 1-PrOH. This resulted in an 86% Zr usageefficiency.

Example 12 (6.7 wt % Zr, Dimeric Zr on Q10)

A support modification as described in Example 5 was performed exceptthat 3.12 g of [Zr(OPr)₃(acac)]₂ was used and 20 ml of heptane was usedinstead of 1-PrOH. This resulted in a 95% Zr usage efficiency.

Example 13 (2.2 wt % Zr, Trimeric Zr on Q30) (Comparative)

A support modification as described in Example 5 was performed exceptthat 1.16 g of Zr(nOPr)₄ (70 wt % in 1-propanol, Sigma Aldrich).Additionally 10 g of silica from Example 2 was used instead of thesilica from Example 1. This resulted in a 100% Zr usage efficiency.

Example 14 (6.0 wt % Zr, Trimeric Zr on Q10) (Comparative)

A support modification as described in Example 5 was performed exceptthat 3.35 g of Zr(nOPr)₄ (70 wt % in 1-propanol, Sigma Aldrich). Thisresulted in a 100% Zr usage efficiency.

Example 15 (8.0 wt % Zr, Pentameric Zr on Q10) (Comparative)

A support modification as described in Example 5 was performed exceptthat 2.67 g of zirconium(IV) ethoxide (97% Sigma Aldrich) was dissolved20 ml of ethanol (anhydrous, Sigma Aldrich) with 1.77 g of acetic acid(glacial, Sigma Aldrich) instead of 1-PrOH. This resulted in a 100% Zrusage efficiency.

Hf Modification of Silica Supports Example 16 (5.4 wt % Hf, Monomeric Hfon Q10)

A support modification as described in Example 5 was performed exceptthat 1.37 g of Hf(iOPr)₄ (99% Sigma Aldrich) was dissolved in 20 ml of1-PrOH along with 1.32 g of acetyl acetone (99% Sigma Aldrich) andallowed to mix for 30 min prior to the introduction of 10 g of silicafrom Example 1. This resulted in a 98% Hf usage efficiency.

Example 17 (7.8 wt % Hf, Monomeric Hf on Q10)

A support modification as described in Example 5 was performed exceptthat 2.00 g of Hf(iOPr)₄ was dissolved in 20 ml of toluene along with1.93 g of acetyl acetone and allowed to mix for 30 min prior to theintroduction of 10 g of silica from Example 1. This resulted in a 100%Hf usage efficiency.

Example 18 (11.8 wt % Hf, Trimeric Hf on Q10) (Comparative)

A support modification as described in Example 5 was performed exceptthat 3.19 g of Hf(iOPr)₄ was dissolved in 20 ml of toluene instead of1-PrOH. This resulted in a 100% Hf usage efficiency.

HRTEM Analysis of Modified Supports Example 19 (HRTEM Analysis ofMonomeric Zr)

High-Resolution Transmission Electron Microscopy (HRTEM) analysis wasperformed on selected modified silica examples. For this, the modifiedsilica was flaked into particles of 100-200 nm thickness using amicrotome. These flaked particles where then mounted onto a copper meshand an antistatic osmium vapour coating was applied. The mounted samplewas then analysed using a Tecnai G2 F20 (manufactured by FEI) intransmission mode. The electron beam was set at an acceleration voltagebetween 100 and 300 kV with a spacing resolution of 1 nm. The electronbeam was focused by a 30 μm diaphragm. HRTEM images were recorded so asto include 50-200 metal nanoparticles in an image at a magnification of25 million times. This analysis was performed on modified silica Example5, Example 7, Example 14, Example 15, Example 17 and Example 18. TheHRTEM images are shown in FIGS. 1-6.

Cs Modification of Modified Supports Example 20 (3.2 wt % Cs, 0.9 wt %Zr, Monomeric Zr)

0.458 g of CsOH.H₂O (99.5% Sigma Aldrich) was weighed out in a gloveboxand dissolved in 20 ml of a 9:1 v/v MeOH:H₂O solvent mixture. 10 g ofthe modified silica from Example 3 was added to the CsOH solution withagitation. Agitation was continued for an additional 15 min after whichthe sample was left for 16 hours in a sealed flask with periodicagitation. After this time the extra-porous solution was removed byfiltration. This was followed by a drying step where the intra-poroussolvent was removed by passing a flow of nitrogen gas over the wetCs/Zr-modified silica at room temperature. Alternatively, theintra-porous solvent was removed on a rotary evaporator at reducedpressure. Following this step, the catalyst beads were placed into adrying oven at 110-120° C. and left to dry for 16 hours. Upon coolingthis yielded the Cs/Zr/SiO₂ catalyst with a 90% Cs usage efficiency. TheCs load (wt %) on the catalyst was determined via powder EnergyDispersive X-Ray Fluorescence analysis (Oxford InstrumentsX-Supreme8000).

Example 21 (3.7 wt % Cs, 0.9 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 20 except that 0.534 gof CsOH.H₂O was used.

Example 22 (4.0 wt % Cs, 0.9 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 20 except that 0.588 gof CsOH.H₂O was used.

Example 23 (4.8 wt % Cs, 0.9 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 20 except that 0.716 gof CsOH.H₂O was used.

Example 24 (5.1 wt % Cs, 1.5 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 20 except that 0.754 gof CsOH.H₂O was used and modified silica from Example 4 was used.

Example 25 (5.7 wt % Cs, 1.5 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 24 except that 0.852 gof CsOH.H₂O was used.

Example 26 (6.7 wt % Cs, 1.4 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 24 except that 1.00 g ofCsOH.H₂O was used.

Example 27 (7.7 wt % Cs, 1.4 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 24 except that 1.17 g ofCsOH.H₂O was used.

Example 28 (9.7 wt % Cs, 2.0 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 20 except that 1.37 g ofCsOH.H₂O was used and modified silica from Example 5 was used.Additionally, the Cs adsorption time was shortened from 16 hours to 2hours with the filtration step being excluded. The excess organicsolvent was dried into the pore volume of the modified silica supportand resulted in a Cs usage efficiency of 100%.

Example 29 (10.2 wt % Cs, 2.0 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 28 except that 1.45 g ofCsOH.H₂O was used.

Example 30 (10.8 wt % Cs, 2.0 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 28 except that 1.54 g ofCsOH.H₂O was used.

Example 31 (11.3 wt % Cs, 2.0 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 28 except that 1.62 g ofCsOH.H₂O was used.

Example 32 (9.2 wt % Cs, 2.4 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 20 except that 1.44 g ofCsOH.H₂O was used and modified silica from Example 6 was used.

Example 33 (10.9 wt % Cs, 2.4 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 32 except that 1.74 g ofCsOH.H₂O was used.

Example 34 (13.0 wt % Cs, 2.3 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 32 except that 2.12 g ofCsOH.H₂O was used.

Example 35 (14.0 wt % Cs, 2.3 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 32 except that 2.30 g ofCsOH.H₂O was used.

Example 36 (12.3 wt % Cs, 3.7 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 20 except that 2.00 g ofCsOH.H₂O was used and modified silica from Example 7 was used.

Example 37 (12.6 wt % Cs, 3.7 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 36 except that 2.05 g ofCsOH.H₂O was used.

Example 38 (13.9 wt % Cs, 3.6 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 36 except that 2.30 g ofCsOH.H₂O was used.

Example 39 (15.4 wt % Cs, 3.6 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 36 except that 2.60 g ofCsOH.H₂O was used.

Example 40 (2.8 wt % Cs, 0.7 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 28 except that 0.37 g ofCsOH.H₂O was used and modified silica from Example 8 was used.

Example 41 (3.4 wt % Cs, 0.7 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 40 except that 0.45 g ofCsOH.H₂O was used.

Example 42 (3.9 wt % Cs, 0.7 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 40 except that 0.51 g ofCsOH.H₂O was used.

Example 43 (4.1 wt % Cs, 1.0 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 20 except that 0.60 g ofCsOH.H₂O was used and modified silica from Example 9 was used.

Example 44 (4.6 wt % Cs, 1.0 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 43 except that 0.68 g ofCsOH.H₂O was used.

Example 45 (5.5 wt % Cs, 1.0 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 43 except that 0.82 g ofCsOH.H₂O was used.

Example 46 (9.1 wt % Cs, 2.0 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 20 except that 1.42 g ofCsOH.H₂O was used and modified silica from Example 10 was used.

Example 47 (9.9 wt % Cs, 1.9 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 46 except that 1.55 g ofCsOH.H₂O was used.

Example 48 (13.8 wt % Cs, 3.3 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 20 except that 2.28 g ofCsOH.H₂O was used and modified silica from Example 11 was used.

Example 49 (15.0 wt % Cs, 3.3 wt % Zr, Monomeric Zr)

A catalyst was prepared as described in Example 48 except that 2.51 g ofCsOH.H₂O was used.

Example 50 (14.0 wt % Cs, 5.7 wt % Zr, Dimeric Zr) (Comparative)

A catalyst was prepared as described in Example 20 except that 2.34 g ofCsOH.H₂O was used and modified silica from Example 12 was used.

Example 51 (15.0 wt % Cs, 5.7 wt % Zr, Dimeric Zr) (Comparative)

A catalyst was prepared as described in Example 50 except that 2.54 g ofCsOH.H₂O was used.

Example 52 (16.1 wt % Cs, 5.6 wt % Zr, Dimeric Zr) (Comparative)

A catalyst was prepared as described in Example 50 except that 2.76 g ofCsOH.H₂O was used.

Example 53 (17.3 wt % Cs, 5.5 wt % Zr, Dimeric Zr) (Comparative)

A catalyst was prepared as described in Example 50 except that 3.01 g ofCsOH.H₂O was used.

Example 54 (6.0 wt % Cs, 2.1 wt % Zr, Trimeric Zr) (Comparative)

A catalyst was prepared as described in Example 28 except that 0.81 g ofCsOH.H₂O was used and modified silica from Example 13 was used.

Example 55 (7.7 wt % Cs, 2.0 wt % Zr, Trimeric Zr) (Comparative)

A catalyst was prepared as described in Example 54 except that 1.06 g ofCsOH.H₂O was used.

Example 56 (13.6 wt % Cs, 5.2 wt % Zr, Trimeric Zr) (Comparative)

A catalyst was prepared as described in Example 28 except that 2.03 g ofCsOH.H₂O was used and modified silica from Example 14 was used.

Example 57 (14.9 wt % Cs, 5.1 wt % Zr, Trimeric Zr) (Comparative)

A catalyst was prepared as described in Example 56 except that 2.26 g ofCsOH.H₂O was used.

Example 58 (16.1 wt % Cs, 5.0 wt % Zr, Trimeric Zr) (Comparative)

A catalyst was prepared as described in Example 56 except that 2.48 g ofCsOH.H₂O was used.

Example 59 (17.3 wt % Cs, 5.0 wt % Zr, Trimeric Zr) (Comparative)

A catalyst was prepared as described in Example 56 except that 2.70 g ofCsOH.H₂O was used.

Example 60 (12.3 wt % Cs, 7.0 wt % Zr, Pentameric Zr) (Comparative)

A catalyst was prepared as described in Example 28 except that 1.82 g ofCsOH.H₂O was used and modified silica from Example 15 was used.

Example 61 (14.0 wt % Cs, 6.9 wt % Zr, Pentameric Zr) (Comparative)

A catalyst was prepared as described in Example 60 except that 2.12 g ofCsOH.H₂O was used.

Example 62 (15.7 wt % Cs, 6.7 wt % Zr, Pentameric Zr) (Comparative)

A catalyst was prepared as described in Example 60 except that 2.42 g ofCsOH.H₂O was used.

Example 63 (18.9 wt % Cs, 6.5 wt % Zr, Pentameric Zr) (Comparative)

A catalyst was prepared as described in Example 60 except that 2.99 g ofCsOH.H₂O was used.

Example 64 (8.8 wt % Cs, 4.9 wt % Hf, Monomeric Hf)

A catalyst was prepared as described in Example 28 except that 1.23 g ofCsOH.H₂O was used and modified silica from Example 16 was used.

Example 65 (10.1 wt % Cs, 4.9 wt % Hf, Monomeric Hf)

A catalyst was prepared as described in Example 64 except that 1.43 g ofCsOH.H₂O was used.

Example 66 (11.4 wt % Cs, 4.8 wt % Hf, Monomeric Hf)

A catalyst was prepared as described in Example 64 except that 1.64 g ofCsOH.H₂O was used.

Example 67 (12.6 wt % Cs, 4.7 wt % Hf, Monomeric Hf)

A catalyst was prepared as described in Example 64 except that 1.84 g ofCsOH.H₂O was used.

Example 68 (11.1 wt % Cs, 6.9 wt % Hf, Monomeric Hf)

A catalyst was prepared as described in Example 28 except that 1.60 g ofCsOH.H₂O was used and modified silica from Example 17 was used.

Example 69 (12.7 wt % Cs, 6.8 wt % Hf, Monomeric Hf)

A catalyst was prepared as described in Example 68 except that 1.86 g ofCsOH.H₂O was used.

Example 70 (14.3 wt % Cs, 6.7 wt5 Hf, Monomeric Hf)

A catalyst was prepared as described in Example 68 except that 2.14 g ofCsOH.H₂O was used.

Example 71 (15.8 wt % Cs, 6.6 wt % Hf, Monomeric Hf)

A catalyst was prepared as described in Example 68 except that 2.41 g ofCsOH.H₂O was used.

Example 72 (13.7 wt % Cs, 10.2 wt % Hf, Trimeric Hf) (Comparative)

A catalyst was prepared as described in Example 20 except that 2.28 g ofCsOH.H₂O was used and modified silica from Example 18 was used.

Example 73 (14.9 wt % Cs, 10.0 wt % Hf, Trimeric Hf) (Comparative)

A catalyst was prepared as described in Example 72 except that 2.51 g ofCsOH.H₂O was used.

Example 74 (16.2 wt % Cs, 9.9 wt % Hf, Trimeric Hf) (Comparative)

A catalyst was prepared as described in Example 72 except that 2.77 g ofCsOH.H₂O was used.

Example 75 (16.0 wt % Cs, 3.4 wt % Zr, 100% Monomeric Zr)

A catalyst was prepared as described in Example 20 except that 2.71 g ofCsOH.H₂O was used and 10 g of modified silica from Example 7 was used.Additionally, after the catalyst had been dried it was crushed using amortar and pestle and sieved into a 0.1-1.0 mm size fraction. Thisresulted in a catalyst with a 100% monomeric content based on wt % Zrbasis.

Example 76 (15.8 Wt % Cs, 3.6 wt % Zr, 79% Monomeric Zr) (Comparative)

A catalyst was prepared as described in Example 75 except that 2.67 g ofCsOH.H₂O was used. Additionally 8.5 g of modified silica from Example 7and 1.5 g of modified silica from Example 14 were used as catalystsupport. This resulted in a catalyst with a 79% monomeric content basedon wt % Zr basis.

Example 77 (15.4 wt % Cs, 3.9 wt % Zr, 61% Monomeric Zr) (Comparative)

A catalyst was prepared as described in Example 75 except that 2.60 g ofCsOH.H₂O was used. Additionally 7 g of modified silica from Example 7and 3 g of modified silica from Example 14 were used as catalystsupport. This resulted in a catalyst with a 61% monomeric content basedon wt % Zr basis.

Example 78 (15.7 wt % Cs, 4.4 wt % Zr, 31% Monomeric Zr) (Comparative)

A catalyst was prepared as described in Example 75 except that 2.66 g ofCsOH.H₂O was used. Additionally, 4 g of modified silica from Example 7and 6 g of modified silica from Example 14 were used as catalystsupport. This resulted in a catalyst with a 31% monomeric content basedon wt % Zr basis.

Example 79 (16.9 wt % Cs, 5.0 wt % Zr, 0% Monomeric Zr) (Comparative)

A catalyst was prepared as described in Example 75 except that 2.92 g ofCsOH.H₂O was used. Additionally, 10 g of modified silica from Example 14were used as catalyst support. This resulted in a catalyst with a 0%monomeric content based on wt % Zr basis.

Example 80 (Catalytic Performance Testing)

Catalysts from Example 20 to Example 79 were tested for the reaction ofmethyl propionate and formaldehyde in a labscale microreactor. For this,3 g of catalyst was loaded into a fixed bed reactor with an internaltube diameter of 10 mm. The reactor was heated to 330° C. andpreconditioning was performed by feeding a vaporised stream comprisingof 70 wt % methyl propionate, 20 wt % methanol, 6 wt % water and 4 wt %formaldehyde from a vaporiser fed by a Gilson pump at 0.032 ml/min. Thispreconditioning was continued overnight. After preconditioning a feedstream comprising of 75.6 wt % methyl propionate, 18.1 wt % methanol,5.7 wt % formaldehyde and 0.6 wt % water, was pumped by a Gilson pump toa vaporiser set at 330° C. before being fed to the heated reactor set at330° C. containing the catalyst. The reactor exit vapour was cooled andcondensed with samples being collected at five different liquid feedrates (between 0.64-0.032 ml/min) so as to obtain conversions at varyingvapour/catalyst contact times. The liquid feed and condensed ex-reactorliquid products were analysed by a Shimadzu 2010 Gas Chromatograph witha DB1701 column. The compositions of the samples were determined fromthe respective chromatograms and yields and selectivities at varyingcontact times determined. Activity was defined as the inverse of thecontact time, in seconds, required to obtain 10% MMA+MAA yield on methylpropionate fed and was determined via an interpolation on a contact timevs. MMA+MAA yield graph. This interpolated contact time was then used toobtain the MMA+MAA selectivity at 10% MMA+MAA yield.

TABLE 1 Activity and MMA + MAA selectivity results for catalyst preparedon the Zr modified support examples with varying Zr nuclearity. Cs:ZrActivity at 10% MMA + MAA Zirconium Zr load Cs load (molar MMA + MAAselectivity Example nuclearity (wt %) (wt %) ratio) yield (1/s) (%)Example 20 1 0.9 3.2 2.4 0.12 95.8 Example 21 1 0.9 3.7 2.8 0.15 97.3Example 22 1 0.9 4.0 3.1 0.18 97.6 Example 23 1 0.9 4.8 3.8 0.24 98.0Example 24 1 1.5 5.1 2.4 0.32 97.4 Example 25 1 1.5 5.7 2.7 0.39 97.1Example 26 1 1.4 6.7 3.2 0.41 97.0 Example 27 1 1.4 7.7 3.7 0.47 97.3Example 28 1 2.0 9.7 3.3 0.45 96.1 Example 29 1 2.0 10.2 3.5 0.39 95.8Example 30 1 2.0 10.8 3.7 0.49 95.8 Example 31 1 2.0 11.3 3.9 0.46 95.5Example 32 1 2.4 9.2 2.6 0.48 96.8 Example 33 1 2.4 10.9 3.2 0.64 96.2Example 34 1 2.3 13.0 3.9 0.67 95.5 Example 35 1 2.3 14.0 4.2 0.75 95.5Example 36 1 3.7 12.3 2.3 0.76 95.3 Example 37 1 3.7 12.6 2.4 0.80 95.0Example 38 1 3.6 13.9 2.7 0.86 94.1 Example 39 1 3.6 15.4 3.0 0.93 94.5Example 40 1 0.7 2.8 2.7 0.13 97.5 Example 41 1 0.7 3.4 3.3 0.17 97.9Example 42 1 0.7 3.9 3.8 0.25 97.8 Example 43 1 1.0 4.1 2.7 0.25 96.3Example 44 1 1.0 4.6 3.1 0.28 97.8 Example 45 1 1.0 5.5 3.7 0.35 96.7Example 46 1 2.0 9.1 3.2 0.47 96.5 Example 47 1 1.9 9.9 3.5 0.71 96.5Example 48 1 3.3 13.8 2.9 0.75 94.5 Example 49 1 3.3 15.0 3.2 0.76 94.8Example 50 2 5.7 14.0 1.7 0.69 93.0 Example 51 2 5.7 15.0 1.8 0.82 93.0Example 52 2 5.6 16.1 2.0 0.85 93.2 Example 53 2 5.5 17.3 2.2 0.68 92.0Example 54 3 2.1 6.0 2.0 0.26 89.2 Example 55 3 2.0 7.7 2.5 0.34 88.8Example 56 3 5.2 13.6 1.8 0.38 85.7 Example 57 3 5.1 14.9 2.0 0.47 88.7Example 58 3 5.0 16.1 2.2 0.51 90.7 Example 59 3 5.0 17.3 2.4 0.41 90.2Example 60 5 7.0 12.3 1.2 0.24 76.0 Example 61 5 6.9 14.0 1.4 0.45 85.0Example 62 5 6.7 15.7 1.6 0.56 87.0 Example 63 5 6.5 18.9 2.0 0.85 87.6

TABLE 2 Activity and MMA + MAA selectivity results for catalyst preparedon the Hf modified support examples with varying Hf nuclearity. Cs:HfActivity at 10% MMA + MAA Hafnium Hf load Cs load (molar MMA + MAAselectivity Example nuclearity (wt %) (wt %) ratio) yield (1/s) (%)Example 64 1 4.9 8.8 2.4 0.51 97.2 Example 65 1 4.9 10.1 2.8 0.58 97.1Example 66 1 4.8 11.4 3.2 0.64 96.5 Example 67 1 4.7 12.6 3.6 0.73 96.5Example 68 1 6.9 11.1 2.2 0.68 96.4 Example 69 1 6.8 12.7 2.5 0.82 96.5Example 70 1 6.7 14.3 2.9 0.88 96.0 Example 71 1 6.6 15.8 3.2 0.88 95.1Example 72 3 10.2 13.7 1.8 0.58 89.8 Example 73 3 10.0 14.9 2.0 0.7191.6 Example 74 3 9.9 16.2 2.2 0.69 91.2

TABLE 3 Activity and MMA + MAA selectivity results for catalyst preparedwith varying amounts of Zr monomer and trimer. Monomeric Zr Cs:ZrActivity at 10% MMA + MAA content (% of Zr load Cs load (molar MMA + MAAselectivity Example Zr content) (wt %) (wt %) ratio) yield (1/s) (%)Example 75 100 3.4 16.0 3.3 1.43 95.8 Example 76 79 3.6 15.8 3.0 1.4494.9 Example 77 61 3.9 15.4 2.7 1.40 93.7 Example 78 31 4.4 15.7 2.51.31 92.0 Example 79 0 5.0 16.9 2.4 1.29 88.6

Example 81 (Accelerated Ageing Tests)

Catalyst sintering resistance was assessed in an accelerated ageingtest. For this, 1 g of catalyst was loaded into a U-tube stainless steelreactor and loaded into an oven. The oven was heated to 385° C. and astream of nitrogen (10 ml/min) was passed through a saturating vaporisercontaining water that was heated to 92° C. This ensured that a feedstream with a water partial pressure of 0.75 bara was passed over thecatalyst heated to 385° C. Periodically the surface area of the catalystsamples was determined ex-situ using nitrogen adsorption/desorptionisotherm analysis (Micromeretics Tristar II). The measured surface areavalues were used to determine sintering rates constants for eachcatalyst and is described as g³·m⁻⁶·d⁻¹. The higher the sinteringconstant, the lower the sintering resistance of the catalyst. This testwas performed on Example 32, Example 38, Example 57 and Example 63.

TABLE 4 Accelerating ageing data for the catalysts of varying Zrnuclearity with comparable activity. Sintering Catalyst rate Surfacearea at time (days) activity constant (g³ · Example 1 7 14 21 28 (1/s)m⁻⁶ · d⁻¹) Example 32 189 187 177 176 178 0.48 1.28E−09 (inventive)Example 38 163 147 144 135 135 0.86 6.35E−09 (inventive) Example 57 218209 192 192 185 0.47 2.26E−09 (compar- ative) Example 63 148 132 124 127119 0.85 8.94E−09 (compar- ative)

Comparative Examples 82 and 83

Examples were prepared according to experimental examples disclosed inEP 1233330. In these examples the silica employed was a gel silica inthe form of spheres of diameter in the range 2-4 mm having a purity ofover 99%, a total surface area of about 300-350 m²/g, and a pore volumeof 1.04 cm³/g with 76% of the pore volume provided by pores having adiameter in the range 7-23 nm.

Two catalysts were prepared by impregnating the silica with an aqueoussolution of zirconium nitrate, sufficient to fill the pores of thesupport, and drying in a rotary evaporator and then in an air oven at120° C. for 2 hours. In one case (example 82), the impregnation of thezirconium solution was assisted by evacuation of the pores of thesupport prior to addition of the solution. In the other case (example83), impregnation of the zirconium solution was carried out in anatmospheric pressure of air. Caesium was then incorporated by a similarprocedure using an aqueous solution of caesium carbonate, to give acaesium content of 4% by weight (expressed as metal). The catalysts werethen calcined in air at 450° C. for 3 hours.

Catalysts were tested under the same conditions as described in example80. One catalyst (example 82) failed to achieve 10% yield andselectivities are shown for the highest obtained yield (9.6%).

TABLE 5 Activity and MMA + MAA selectivity results for comparativeexamples 82 and 83. Zr Cs Cs:Zr Activity at 10% load load (molar MMA +MAA MMA + MAA Example (wt %) (wt %) ratio) yield (1/s) selectivity (%)Example 1.7 4.0 1.6 0.05 65.2 82 Example 1.7 4.0 1.6 0.12 73.2 83

HRTEM Results for Zr and Hf Modified Silica Supports

The HRTEM images (Example 19) for the Zr and Hf modified silica examples(Example 5, Example 7, Example 14, Example 15, Example 17 and Example18) are shown in FIG. 1 to FIG. 6. In the case of the HRTEM images ofmonomeric Zr and Hf, it is difficult to distinguish clear Zr or Hfparticles and this is indicative of very small Zr/Hf nanoparticlespresent on the modified silica surface. This is due to the Zr or Hfbeing present as monoatomic atoms. In the case of the trimeric Zr or Hfand pentameric Zr examples, clear Zr or Hf clusters can be distinguishedon the modified support HRTEM images. This data shows that the solutionphase nuclearity of the Zr or Hf species is transferred from solution tofinal catalyst formulation.

Graphed Data

Activity and Selectivity Data Constructed from Table 1 and Table 2

The MMA+MAA selectivity (%) vs. catalyst activity for the catalystsprepared in Example 20 to Example 74 is shown in FIG. 7. From this graphit is clear that the trimeric Zr and Hf as well as pentameric Zr resultsin lower MMA+MAA selectivity across the entire activity range examined.The dimeric Zr catalyst show improved selectivity compared to thetrimeric Zr catalysts at comparable Zr and Cs loadings.

Activity and Selectivity Data Constructed from Table 3

The catalyst selectivity for mixed monomer/trimer catalysts prepared inExample 75 to Example 79 is shown in FIG. 8. The Zr monomer is contentis calculated as the % of Zr content present as monomer. In theseexamples the catalyst was crushed and sieved to 0.1-1.0 mm particles inorder to increase sample homogeneity. From this graph it is clear thatdecreasing amounts of Zr monomer in the formulation will result in adecreasing MMA+MAA selectivity.

Sintering Resistance Data Constructed from Table 4

The catalyst sintering constants as determined by the advanced ageingtest described in Example 81 is shown in FIG. 9. From FIG. 9 it is clearthat monomeric Zr catalysts display lower sintering rates at comparablecatalyst activity.

Attention is directed to all papers and documents which are filedconcurrently with or previous to this specification in connection withthis application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings) may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends to any novel one, or any novelcombination, of the preferred, typical or optional invention featuresdisclosed in this specification (including any accompanying claims,abstract or drawings), or to any novel one, or any novel combination, ofthe preferred, typical or optional invention steps of any method orprocess so disclosed.

1. A method of producing an ethylenically unsaturated carboxylic acid orester, comprising the steps of contacting formaldehyde or a suitablesource thereof with a carboxylic acid or ester in the presence ofcatalyst and wherein the catalyst comprises a modified silica support,comprising a modifier metal and a catalytic metal on the modified silicasupport, wherein the modifier metal is selected from the groupconsisting of zirconium and hafnium, characterised in that at least aproportion of the modifier metal is present in modifier metal moietieshaving a total of up to 2 modifier metal atoms or is derived from amonomeric and/or dimeric modifier metal cation source at thecommencement of the modification.
 2. A method according to claim 1,wherein the carboxylic acid or ester is of the formula R¹—CH₂—COOR³,wherein R¹ is hydrogen or an alkyl group with 1 to 12 carbon atoms andR³ is independently, hydrogen or an alkyl group with 1 to 12 carbonatoms, and the formaldehyde or a suitable source of formaldehyde is offormula (I) as defined below:

where R⁵ is methyl and R⁶ is H; X is O; m is 1; and n is any valuebetween 1 and 20 or any mixture of these.
 3. A method according to claim1, wherein the carboxylic acid or ester is selected from methylpropionate and propionic acid.
 4. A method according to claim 1, whereinthe step of contacting formaldehyde or a suitable source thereof with acarboxylic acid or ester in the presence of catalyst is also in thepresence of an alcohol.
 5. A method according to claim 4, wherein thealcohol is methanol.
 6. A method according to claim 1, wherein theethylenically unsaturated carboxylic acid or ester is selected from thegroup consisting of methyl methacrylate and methacrylic acid.
 7. Amethod of producing a modified silica support for a catalyst comprisingthe steps of: i. providing a silica support with isolated silanolgroups; ii. contacting the silica support with a monomeric and/ordimeric zirconium or hafnium modifier metal compound to effectadsorption of the modifier metal onto the support; and iii. calciningthe modified silica for a time and temperature sufficient to convert themonomeric and/or dimeric zirconium or hafnium compound adsorbed on thesurface to an oxide or hydroxide of zirconium or hafnium.
 8. A method ofproducing a catalyst comprising the method of claim 7, further includesthe step of treating the calcined modified silica with a catalyticalkali metal to impregnate the modified silica with the catalytic metalto form the catalyst.
 9. A method according to claim 7, whereinadsorption onto at least 25% of the isolated silanol groups is effected.10. A method according to claim 8, wherein the catalytic metal is atleast one or more alkali metal.
 11. A method according to claim 8,including the step of calcining the catalyst formed in step iii.
 12. Amethod according to claim 7, and including the step between step ii andiii of removing any solvent or liquid carrier for the modifier metalcompounds.
 13. A method according to claim 7, and including the step ofdecreasing the concentration of the silanol group prior to treatmentwith the modifier metal compounds by calcination treatment, chemicaldehydration or other suitable methods.
 14. A method according to claim7, wherein the modifier metal cation source is a solution of thecompounds so that the compounds are in solution when contacted with thesupport to effect adsorption onto the support.
 15. A method according toclaim 14, wherein the solvent for the solution is other than water. 16.A method according to claim 7, wherein one or more non-labile ligandsare attached to the modifier metal cations to at least partially formthe said compounds and are selected from molecules with lone paircontaining oxygen or nitrogen atoms able to form 5 or 6 membered ringswith a zirconium or hafnium atom, including diones, diimines, diamines,diols, dicarboxylic acids or derivatives thereof such as esters, ormolecules having two different such functional groups and in either casewith the respective N or O and N or O atom separated by 2 or 3 atoms tothereby form the 5 or 6 membered ring.
 17. A method according to claim16, wherein the non-labile ligands form complexes with the monomericand/or dimeric modifier element.
 18. A method according to claim 7,wherein the silanol concentration on the silica support when contactedwith the modifier metal compound is 0.1-2.5 silanol groups per nm². 19.A method according to claim 7, wherein at least 25% of the modifiermetal in the modifier metal compounds are in monomeric and/or dimericmodifier metal compounds when the source thereof is contacted with thesupport to effect adsorption of the compounds onto the support.
 20. Amethod according to claim 7, and including the step of drying orcalcining the silica support prior to treatment with the modifier metalcompounds.
 21. A method according to claim 7, wherein the silica is inthe form of a gel prior to treatment with the modifier metal compounds.22. A method according to claim 7, and including the step of dispersingthe modifier metal onto the internal and external surfaces of the silicasupport by adsorption.
 23. A method according to claim 7, wherein themodifier metal compound is in the form selected from the groupconsisting of zirconium(IV) acetylacetonate (zirconium,tetrakis(2,4-pentanedionato-O,O′)), zirconium(heptane-3,5-dione)₄,zirconium(2,2,6,6-tetramethyl-3,5-heptanedione)₄, zirconium(IV) ethyl3-oxobutanoate, zirconium(IV) t-butyl 3-oxobutanoate, or zirconium(IV)i-propyl 3-oxobutanoate in one of methanol, ethanol, isopropanol,propanol, butanol, isobutanol, or 2-butanol with up to 20% water byvolume or selected zirconium (pentane-2,4-dione)₄, zirconium(ethyl3-oxobutanoate)₄, zirconium(heptane-3,5-dione)₄,zirconium(2,2,6,6-tetramethylheptane-3,5-dione)₄,zirconium(propoxide)(pentane-2-3-dione)₃,zirconium(propoxide)₃(2,2,6,6-tetramethyl-3,5-heptanedione)(zirconium(Butyl)₃(t-butyl 3-oxobutanoate), zirconium(Ot-butyl)₂(t-butyl3-oxobutanoate)₂ and metal salts such as zirconium perchlorate,zirconium oxynitrate and zirconium oxychloride.
 24. A method ofproducing a modified silica support comprising the steps of: i.providing a silica support having silanol groups; and II. treating thesilica support with monomeric and/or dimeric modifier metal compounds sothat modifier metal is adsorbed onto the surface of the silica supportthrough reaction with silanol groups, wherein the adsorbed modifiermetal atoms are sufficiently spaced apart from each other tosubstantially prevent oligomerisation thereof with neighbouring modifiermetal atoms.
 25. A method according to claim 24 wherein the spacingapart of the modifier metal atoms is effected by: i. decreasing theconcentration of silanol groups on the silica support; and/or ii.attaching a non-labile ligand of sufficient size to the modifier metalcation.
 26. A method according to claim 24, wherein the adsorbedmodifier metal atoms are sufficiently spaced apart from each other toprevent trimerisation with neighbouring modifier metal atoms thereof.